An electromagnetic coil assembly typically includes a case. Internal to the case is a spindle with a conductor or wire wound around the spindle. The conductor is typically helically wound around the spindle. One example of use of electromagnetic coil assemblies such as these is in combination with drug pumps and drug delivery control valves. FIG. 1 shows a sectional view of a prior art electromagnetic coil assembly used in such devices, and reference may be made to U.S. Pat. No. 6,264,439 for a more detailed description thereof.
Briefly, the prior art electromagnetic coil assembly shown in FIG. 1 has a case 20, and internal to the case is a spindle 12. The case 20 is typically a manufactured part made by a turning process, and the case defines an opening that is symmetric about an axis of revolution. The spindle 12 is also typically a turned part that is symmetric about its principal axis and is of ferromagnetic material. The wire coil or conductor winding 14 is helically wound around a central portion of the spindle, and when current passes through the coil an electromagnetic field is generated. The prior art electromagnetic coil assembly also includes a washer 16 pressed onto one end of the spindle and a locater or spacer 18 pressed onto the other end of the spindle. The washer and locater are press fit onto opposite ends of the spindle and held thereon by a friction fit. Fixturing is employed to hold all the components in place while the case is being filled with a potting compound or epoxy 24, and while the epoxy cures. The epoxy is added in two separate phases or steps. The case is then fitted to an electromagnetic device 26.
In the prior art, the combination of the washer and the locator serve to center the spindle within the case. The washer, however, does not fully constrain the spindle, and the spindle can therefore travel, along with the associated washer, in the direction of its principal axis. When the coil case is filled with potting epoxy, the spindle is locked in position. Furthermore, if there is no locator, the free end of the spindle opposite the washer additionally must be held concentric with the case and constrained in the axial direction until the potting compound has cured. Fixturing establishes the distance from the washer end of the spindle to the plane established by the washer end of the case.
What is needed is an improved electromagnetic coil assembly and method that does not require washers, provides for improved stability of components, decreases production time, and reduces fixturing requirements.